In many types of rotating rigid disk files, each of the read/write transducers (or heads) is supported on a carrier (or slider) which rides on a cushion or bearing of air above the surface of its associated disk when the disk is rotating at its operating speed. The slider has an air-bearing surface (ABS), typically in the form of a plurality of rails, and is connected to a linear or rotary actuator by means of a relatively fragile suspension. There may be a stack of disks in the disk file with the actuator supporting a number of sliders. The actuator moves the sliders radially so that each head may access the recording area of its associated disk surface.
In these conventional disk files the slider is biased towards the disk surface by a small force from the suspension. The ABS of the slider is thus in contact with the disk surface from the time the disk fib is turned on until the disk reaches a speed sufficient to cause the slider to ride on the air-bearing. The ABS of the slider is again in contact with the disk surface when the disk file is turned off and the rotational speed of the disk falls below that necessary to create the air-bearing. In order to provide wear resistance for the ABS, a protective overcoat may be placed on the slider rails. Assignee's U.S. Pat. No. 5,159,508 describes a slider wherein the air-bearing rails have an amorphous carbon overcoat which is adhered to the slider material by a silicon adhesion layer.
The disk for use in such CSS rigid disk files is a thin film metal alloy disk which typically comprises a substrate, such as an aluminum-magnesium (AlMg) alloy with a nickel-phosphorous (NiP) surface coating, and a cobalt-based magnetic alloy film formed by sputter deposition over the substrate. A protective overcoat, such as a sputter-deposited amorphous carbon film, is formed over the magnetic layer to provide corrosion resistance and wear resistance from the ABS of the slider. Assignee's U.S. Pat. No. 4,778,582 describes a protective hydrogenated disk carbon overcoat formed by sputtering a graphite target in the presence of Ar and hydrogen (H2).
In such contact start/stop (CSS) disk files a liquid polyperfluoroether lubricant is also maintained on the surface of the protective disk overcoat to prevent damage to the head and the disk during starting and stopping of the disk. Typically, the lubricant used on disks with carbon overcoats is made up of a first layer of lubricant which is bonded to the carbon and a second layer of free or mobile lubricant on top of the bonded lubricant.
In order to improve the wear resistance of the disk, as well as to maintain consistent magnetic properties, it is desirable to make the disk surface as smooth as possible. However, a very smooth disk surface creates an additional problem in CSS disk files, which is referred to as "stiction". This means that after the slider ABS has been in stationary contact with the disk for a period of time, the slider tends to resist translational movement or "stick" to the disk surface. It is known that this "stiction" force can increase over time. Thus the stiction force measured relatively soon after a CSS cycle is referred to as "CSS stiction", while that measured several hours after a CSS cycle is referred to as "rest stiction". Stiction is caused by a variety of factors, including static friction and adhesion forces between the disk and slider created by the lubricant, typically the mobile lubricant. Stiction in a CSS disk file can result in damage to the head or disk when the slider suddenly breaks free from the disk surface when disk rotation is initiated. In addition, because the suspension between the actuator and the slider is relatively fragile in order to permit the slider to fly above the disk surface, sudden rotation of the disk can also damage the suspension.
What is needed is an improved slider which reduces stiction and thus improves the head-disk interface in a CSS disk file.